Experimental Study On Shear Behavior Of Interface Between Loess And Structure

The application of pile foundation in loess area is increasingly widespread.The shear characteristics of pile-soil interface directly affect the bearing capacity of pile foundation.The interface parameters of pile-soil are important engineering design parameters,which are difficult to determine at present.Based on this,this paper takes the concrete-soil interface as the object,and uses Shear Trac-III large direct shear instrument to carry out research work on the shear characteristics of the interface between loess and concrete.When normal stress is relatively small,the shear strength of interface under consolidation condition firstly increases and then decreases with the increase of initial moisture content of loess,and finally approaches a constant.When normal stress is relatively big,the shear strength of interface under consolidation condition decreases with the increase of initial moisture content,and finally approaches a constant,and so does the shear strength of interface under unconsolidation condition regardless of the value of the normal stress.With the increase of initial moisture content,the cohensive force of interface firstly increases and then decreases under both consolidation and unconsolidation conditions,while the internal friction angle decreases and finally approaches a constant.With the increase of shear rate,the shear stress of interface decreases gradually.Influences of shear rate on shear characteristics of loess-concrete interface become more obvious when normal stress and moisture content of soil increase.The cohensive force and the internal friction angle of interface will be greatly decreased because of slurry.All shear stress-shear displacement curves under various slurry thicknesses have the softening form,and with the increase of slurry thickness,both the degree of softening and the shear stress decrease gradually.With the increase of slurry thickness,the cohensive force of interface decreases gradually,and its changing rate decreases too,while the internal friction angle changes a little.Under various normal stresses,the shear strength of the interface increases with the increase of the initial dry density of the soil sample.With the increase of normal stress,the effect of the initial dry density of the soil sample on the shear strength of the interface is significantly increased.Based on the experimental results,it is found that the shear stress-shear displacement curves obtained in this paper can be divided into strain softening type,softening-linear hardening type,strain hardening type and hardening-linear hardening type according to their shape characteristics.under conditions of no slurry,whether the softening of the front section of the shear stress-shear displacement curve is mainly affected by normal stress,and whether linear hardening occurs in the middle and posterior section is mainly affected by the initial moisture content of the soil.Combining the strain softening constitutive model and the hyperbola with the tri-fold line model,a softening-linear hardening model and a hyperbolic-linear hardening model which can effectively represent the linear hardening of the latter part of the curve are proposed.The calculation results of the model are in good agreement with the experimental results.